Apparatus for automatically reproducing contours



Dec. 23, 1952 Filed Feb. 13. 1947 w. L. MARTIN 2,622,871

APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS l0 Sheets-Sheet 1 ESE 29 51 2? 2 26% g as 16 20 3 A a A. 1 12 E V I a L] 1l| j 45% 1|| du 2'0 A INVENTOR. a

WENDELL L. MARTIN F1 5. 1 2 3 ATTORNEYS APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13. 1947 10 Sheets-Sheet 2 170 174 F1612 F1613 1 INVENTOR.

171 WENDELL L. MARTIN i 169 172 BY WWW [IT TO PNE'YS Dec. 23, 1952 w. 1.. MARTIN 2,622,871

APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13, 1947 10 Sheets-Sheet 3 IN VEN TOR. \A/ENDELL L. MARTIN gM+M ATTOPNm Dec. 23, 1952 'w.1 MARTIN 2,622,871

APPARATUS FQR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13, 1947 I 10 Sheets-Sheet 4 INVENTOR. WENDELL L. MARTIN ATTORNEY 5.

W. L. MARTIN Dec. 23, 1952 APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13. 1947 10 Sheets-Sheet 5 J W E WENDELLL. MAR'TIN ATTORNEYS 23, 1952 w, -rm 2,622,871

APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13, 1947 10 Sheets-Sheet 6 INVENTOR. 52 WENDELL L. MARTIN ATTOPJVEYS.

APPARATUS FOR AUTOMATICALLY REPRODUCING comouas Filed Feb. 15, 1947 W. L. MARTIN Dec. 23, 1952 I 10 Sheets-Sheet 7 INVEN TOR. WENDELL L. MARTm ATTORNEYS.

Dec. 23, 1952 w. L. MARTIN 2,522,371

APPARATUS FOR AUTOMATICALLY mjpnonucmc CONTOURS Filed Feb; 1:, 1947 10 Sheets-Sheet 8 PLATE VOLTAGE 0N TUBES I99 AND 200 VOLTAGEACROSS PHASE SHIFT BRIDGE I97 VOLTAGE BETWEEN I96 AND l9l VOLTAGE BETWEEN !96 AND EOI EP a+c MODIFIED "Ill C "IN. D

a a MODIFIED v TUBE 20o TUBE 199 (INCREASES OVERLAF) (DEcREAsEs OVERLAP) 17 I INVEN TOR. WENDELL L. MARTIN J BY ATTORNEYS.

W. L. MARTIN Dec. 23, 1952 APPARATUS FOR AUTIQMITICALLY REPRODUCING CONTOURS v 10 Sheets-Sheet 9 IN VEN TOR. WENDELL L. MARTIN warn/7Z5 Filed Feb. 13, 1947 ATTORNEYS Dec. 23, 1952 w. L. MARTIN 2,622,871

APPARATUS FOR AUTOMATICALLY REPRODUCING CONTOURS Filed Feb. 13, 1947 10 Sheets-Sheet 10 PLATE VOLTAGE ON TUBE \99 PLATE VOLTAGE ON TUBE 200 GRID CONTROL VOLTAGE ACROSS 278 SHOWING CHANGE FROM "NO coNTAcT" PLATE VOLTAGE QN TUBE 199 VOLTAGEACROSS 278 FOR E No cONTAcT" VOLTAGE ACROSS 275 FOR U CONTACT PLATE VOLTAGE ON TUBE. 20o

/ TUBE \99 TUBE 200 (TUBE I99 TUBE 200 S m o INVENTOR. H WENDELL L. MARTIN ATTORNEYS Patented Dec. 23, 1952 .UNITED STATES PATENT OFFICE APrAnATUs, FOR AUTOMATICALLY REPRODUCING CONTOURS W'ntlell L. ,Martin, Shaker Heights, Ohio, assignor to The Martin Brothers Electric Company, Cleveland,- Ohio, a corporation of Ohio Applicationl iebriiary 12, 194i; Sena-'1 No; 721:;223

(Cl. tee-2'3) 32' Glaims.

This invention mates to an apparatus for reproducing contours a d particularly to a f tus comprising a tracer acapccd a-iitoinatially to follow a contour of pattern, the Iriotiofi ofthe tracer being trans-mitten to atool such as a cutting torch, for iar'riplywhioh iistraified to follow the same path as the tracer, thereby to reproduce the contour i pattern.

The present inventioninvolves several instrumentallti es' Whih cooperate to producea high 1y advantageousapparatus; The several iiis'tru mentalities; however, may be useful separately or in combination with ot iii'st'furhentalities Thus, the apparatus com ss a line renewing mechahishi or tracer arranged to renew a mic or pattern and depending for its" action upon the flow of electric eurr'erit Between a trader and the line or pattern; Through appropriate lc tlic Circuit s, the traceris d-i'ivf-i along the line iii Such manner as: to airitaifithe amount of overlap hot-ween line and tracer substantially constant. The electrical-1- apparaics is preferably operated on alternatingcurremwith circuits arranged so that co tiiig'i pulses-are applied to the steering rhe'ciia m'at last at frequency of'the power cirixi-t, with an ordinary 60 cycle pOW'l'" Supp-I57} i are atleast 66 correctingimpu-ISes pe 'hd, a high degreeof accuracy 21-h 6f cti'o'fi of errorsbefore the errors become Page; this accuracy can be increased systems in which a power supply of higher frequency is eihployed The driving mechanism is arranged, according to the preferred form or my invention, in such manner that there is no contact re' uiree between a driving wheel or the like and the pattern. Mechanism is provided for interconnecting thefol-lower with a carriage supporting a cutting torchor the like whereby the torch may'be fiioved accurately with thetracer. This mechanism is' preferably arranged; so that the tracer and the torch maybe vertically aligned} with the pattern interposed between therii', and the workpiece disposed beneath the torch anclin vertical alignment with the pattern, thus providing a compact apparatus. Provision is made also whiebv' the trace?- and torch can travelover a pattern-o1 large area'w-ithout requiring floor space'for theap'pai'atu's greatly in excess of the space required for the work piece or pieces. The arrangement" preferably is such as to permit thmachine to operateonone workpiece whileanother workpiec'e-- is being placed in position within the apparatus for the next operation;

A general ob'ec't of theinventlori is the mm 2 vision of a contour reproducing machine which is adapted to operate rapidly and accurately to reproduce a pattern or contour, Another object is the provision of a Inachineadapted accurately to follow a line or contour having-an electrical conductivity different f-roih that of the back-- ground; material on which the contour is laid out. Another object is the provision of simple efiicient electrical circuits for such dvices which will result ihthe accurate control of the line follower without substantial hunting or deviation from the contour; Further objects are the provision of mechanisms and circuits whereby the starting of the apparatus is made siinpl'e, and the provision of means whereby the follower may be; driven along the contour constantly at the desired-lineal speed. other objects include the provisionpf an automatic line following apparatusinwhich the line follower isdriven mm; the contourby driving means which require no contact with the pattern itself; theprovision of contour cutting pparatus in which one workpiece ;can-be operated upon while another is beingplaced in position for subsequent operation; the-provisionof a contour cutting machine in which the line following nechanisni, pattern, torch and workpiece are all vertically aligned, thus greatly reduoingthe floor space required by the apparatus as compared with the floor space required by prior devices adapted to work on materials-of corresponding size;

Further objects and advantages of the' inven-' ti-ohwill become apparent from the following description of preferred forms thereof", reference being made to the accompanying drawings in which Figure 1 is a plan view of a prefer'red form of apparatus; Figure 2- is an end elevation of the apparatus shown in- Figure 1, the view beiiig taken as inciicated by line 2-4 of Figure l; Figureii' is a side elevation of the apparatus shown in-Figure 1, the view being taken as in dicated by the liiie 3-3 of Figure 1; Figure 4 is a' side elevationa-l view on an enlarged scale showing thamechariism for interconnecting the carriage which supports the tracer and its drive mechanism an-dih'e torch supporting: carriage; Figure 5 is end. elevational View of the sain'e me Janisnit,v the view being taken as indicated bvthe lihe 5 5 of Figure 4;- Figur'e 6 is 'a' side eicvati'onal' view chair enlarged scale" showing Figure 9 is a view looking down on the carriage and illustrating the driving and steering connections, the View being taken along the line 9-4 of Figure 6; Figure 10 is a sectional detail on an enlarged scale taken along the line Iii-iii of Figure 6 and illustrating one of the carriage drive spindles; Figure 11 is a diagrammatic view illustrating the drive for the tracer carriage; Figure 12 is a detail of the follower and its supporting spindle; Figure 13 is a detail as indicated by the line l3-l3 of Figure 12 and showing the rela tionship between the follower point and the contour which is to be followed; Figure 14 is a wiring diagram of a preferred electrical circuit for the apparatus; Figure 15 diagrammatically illustrates the operation of the circuit of Figure 14 under varying conditions of operation; Figures 16 and 17 illustrate a modified form of follower; Figure 18 is a wiring diagram of a preferred type of circuit for use with the modified follower; and Figure 19 diagrammatically illustrates the operation of the circuit of Figure 13.

General arrangement The general arrangement of the apparatus is illustrated in Figures 1, 2 and 3. As there shown, the supporting structure comprises a series of vertical supports l0, which may be set into the floor as shown, and to the upper ends of which are secured horizontal angle irons ll carrying longitudinally extending tracks [2. Preferably the supporting frame is unobstructed at its ends to facilitate positioning of the workpieces. The tracks i2 function to support the movable main frame indicated in general at 15 and comprise end members If; extendin parallel with the rails 52, and transversely extending rails l1 and IS, the movable main frame being supported on the rails (2 by rollers l9 and 20. It will be noted that the rollers 23 are grooved to retain the main frame on the supporting tracks [2. The movable main frame carries a pattern support 25 adapted to receive a pattern 25. The main frame rails i! and i8 carry the sub-frame indicated in general at El, the sub-frame comprising end members 28 and sub-frame rails 29 and 33 extending at right angles to the main frame rails 11 and E3; the main or follower carriage indicated in general at 3! is supported on the sub-frame rails. The carriage is movable along the sub-frame rails 23 and 3t, and the sub-frame 21 is movable along the main frame rails I1 and I8. Hence the carriage can be moved in such a manner that the follower carried thereby will reach substantially all points of the pattern support 25 within the marginal portions thereof.

As shown particularly in Figures 3 to 5, the sub-frame 27 also includes rails 33 and 34 which extend parallel to the tracks 29 and 30 beneath the pattern support 25. Tracks 33 and 34 support the tool carriage indicated in general at 35, which carries any suitable cutting tool marking device or the like, a cutting torch 36, which may he of conventional construction, being shown in the present embodiment.

In order to support the work in position for cutting, I provide a work-support comprising vertical members 38, horizontal members 39 and work-engaging angle irons 40 which directly support the work such as the workpieces W and W. The main frame is arranged to be moved manually from one working position to another and may be locked in position by the toggle brake mechanism shown in Figures 1 and 2 and consisting of a handle member 42 pivoted as at 43 to a bracket supported by the frame member [6 having an end portion 44 pivotally connected to the toggle link 45, which in turn is pivoted to one end of the brake member 46, the opposite end of the member 46 being secured to the underside of the pattern support 25 as at 41. Downward movement of the handle urges the brake member tit into engagement with the upper surface of one of the tracks [2 and thus frictionally locks the main frame against movement with respect to the tracks. In its locked position, the toggle links 44 and 45 are moved over center to retain the brake member ie against the track.

It will be noted that inasmuch as the tracks [2 and the associated parts of the supporting structure may be indefinitely long and preferably are more than twice as long as the end members l6 of the main frame i5, the main frame can be positioned adjacent one end of the apparatus, for example, as shown in Figures 1 and 3, and the apparatus may be operated to cut a pattern in a workpiece W while another workpiece W is being placed in position on the work supporting members 40'. The work support and main supporting structure thus provide two working stations, thereby increasing the productive capacity of the apparatus.

In order to move the torch over a workpiece and thereby to cut a desired contour, the main carriage 3! is provided with an automatic line follower or tracer, preferred forms of which are described in detail below, so that the carriage will automatically follow a line or contour. The components of the motion of the carriage 31 in directions parallel to the main frame rails I1 and I8 result in movement of the sub-frame 21 along the tracks I! and I8 and corresponding movement of the tool or torch carriage 35. The components of the motion of the carriage 3| in directions normal to the tracks I! and I8, i. e., parallel to sub-frame rails 29 and 30, are transmitted to torch carriage 35 by the mechanism shown particularly in Figures 3, 4 and 5.

As shown in those figures, the main carriage 3! includes a base 58 provided with a pair of grooved wheels 5| engagin the square track-29 and a plain wheel 52 engaging the track 3!] and arranged to drive the carriage along the tracks 23 and 35 in accordance with the requirements of the contour being reproduced. Power for the carriage is supplied through flexible cable 53, the electronic components of the carriage control being disposed within the housing B l, the end surface 5-4 of which comprises a control panel.

The torch supporting carriage 35 is disposed on the tracks 33 and 34 immediately beneath the main carriage 5E]. The carriage 35 comprises a base 55 provided with a pair of grooved wheels 5t engaging the square track 34 and a plain roller 57 engaging the angle iron track 33 (see Figure 4). The base also is provided with a collet or clamp 58 in which the downwardly extendin rod 59 is adjustably supported. The rod 59 in turn carries the torch 36 by means of the adjustable supporting bracket 60. vertically by the knob GI and is supplied with acetylene gas, low pressure oxygen and high pressure oxygen through the flexible hoses 62, 63 and 54, respectively, the hoses extending over the torch carriage 35, resting on the base 55 and connecting with distributor head 65 from which conduits extend through suitable control valves, including a solenoid valve 222 for controlling the high pressure oxygen as hereinafter described, to the supply tanks for the various gases.

The torch is adjustable As noted above, components of the motion of the main carriage in directions parallel to the tracks I1 and 18 are transmitted directly to the torch carriage 35 because the tracks 33 and 34 are rigidly supported by the end frame members 28 of the sub-frame 21. However, it is not possible to make a direct vertical connection for transmitting the motions oi the main carriage along the tracks 29 and 30 to the torch carriage, because the pattern support and the pattern 26 are interposed between the carriages. In order to transmit these motions of the main carriage to the torch carriage, the two carriages are interconnected by chains 66 and 61, each chain having its ends connected to opposite ends of the main and torch carriage, and the chain 66 passing around the sprockets 1B and 1| and the-chain 61 passing around sprockets l2 and 13. All of these sprockets are mounted in the end frame members '23 of the sub-frame 21. In Figure 4 of the drawings, the chains are shown as diverging slightly for convenience in illustration. In practice, the reaches of the chains between the sprockets are substantially parallel.

It will be seen that by this arrangement, motions of the carriage 3| along the tracks 29 and 30 are transmitted accurately to the carriage 35. Movement of the carriage 31 to the right in Figure 4, for example, will pull the chain 65 around the sprockets it and H, and thus pull the carriage 35 in the same direction at the same speed and for the same distance as the cariage 50. During motion to the right, the chain 6'! is held taut by the pull exerted by carriage '35 on it. When the carriage 50 moves in the opposite direction, the chain 5'! is pulled over sprockets 12 and 13, thus transmitting the motion of carriage 3| to carriage 35 in the opposite direction. At the same time, the chain '66 is held taut by the carriage 35. Thus, the torch carriage accurately follows the movements of the main carriage.

Main carriage drive The motion of the main carriage 3| along the contour, as shown particularly in Figures '6 and '7, is produced by two motors which are mounted thereon-a driving motor 15, which propels the carriage at substantially constant speed, and a steering motor It, which steers the carriage in accordance with signals received from a tracer or follower point H in order to cause the carriage to move in such a path that the tracer automatically is maintained in contact with the contour which is to be reproduced.

The electrical circuits whereby the operation of the steering motor is controlled will be described in detail below. For present purposes, it is sufficient to state that the tracer or follower ll is carried bythe shaft 18 of the steering motor it. The tracer is offset slightly from the centerof the shaft, the driving arrangement being such that a line drawn through the centers of the shaft and tracer will indicate the direction of movement of the carriage. The electrical circuits actuate the steering motor to maintain a predetermined amount of overlap between the tracer point H and a contour C of the pattern 25, as shown in Figure l3. The steering motor shaft 18 rotates the point H at the same time that it steers the driving mechanism, thus maintaining the correct relationship between the direction of movement of the carriage and the position of the off-set tracer point with respect to the center of the shaft 1-8.

While it is possible to operate my deviceby employing a single driving wheel driven by the driving motor and mounted on a spindle steered by the steering motor to determine the direction of movement, such an arrangement ordinarily requires that the driving wheel operate on the pattern. This is undesirable because of the resultant wear on the pattern. Accordingly, I preferably employ an arrangement .such as shown in the drawings wherein the driving forces ofthe carriage are exerted on the main frame tracks I and i8 and the sub-frame tracks 29 and 3&1. As these tracks extend at right angles to each other, the motion of the carriage over the pattern in any direction can be resolved into components in directions parallel to the respective tracks.

Ihe movement of the carriage is separated into its two components one parallel to tracks I! and 18 and one parallel to tracks 29 and .30, and the proper driving forces are exerted on the tracks by mechanism embodying steerable driving spindle assemblies 89 and 81 provided with intermediate driving wheels 82 and '83, respectively. The position of the spindles is controlled by mechanism hereinafter described so that the'intermedia'te driving wheels are always disposed in planes parallel to each other. The intermediate driving wheels frictionally engage friction wheels 83 and 85, respectively, which are disposed at right angles to each other. The wheel 8 has a sliding engagement with a suitable square shaft 86 and thus drives the main drive wheels 88 and 89 which engage the main frame tracks I! and vI8 (see Figure 1) while the wheel 85' drives the drive roller 52 through the shaft 90, the roller 52 being in engagement with the track 30 as previously described (see Figures 3, 6 and 7).

The intermediate drive wheels 82 and '83 are driven at the same substantially constant speed by the drive motor 15, and the spindles and 8|, upon which they are mounted, are steered by the steering motor 15 so that the planes .in which the intermediate drive wheels lie are always parallel to the desired direction of movement of the carriage as determined by the contour. The manner in which such a driving and steering arrangement results in the desired motion of the carriage will be evident from the diagrammatic illustration in Figure 11. There, in the full line position, the intermediate driving Wheels 82 and 83 are disposed to lie in the plane of friction wheel 84. In this position, rotation of the intermediate wheel 82 will result in rotation of the friction wheel 84 at the same peripheral speed. The wheel 84 drives the drive wheels 68 and 89 through the shaft 86 and thus moves the carriage in a direction parallel to the rail or track I8. Thus, in the embodiment shown, the carriage and the entire sub-frame will move along the rail 18 at a speed directly proportional to the peripheral speed of the drive wheel 82, but less than that speed because the giaheel 89 is of smaller diameter than the wheel With the wheel 62 lying in the same plane as the wheel 84, the wheel 83 which also lies in that same plane is necessarily disposed at right angles to the wheel 85. In this position, the wheel 83 merely slides on the serrated surface of the wheel without any resultant rotation of the wheel 85. Thus, the only motion of the carriage is in a direction parallel to the rails I1 and I8. If the planes of the intermediate driving wheels were rotated 90, then wheel 82 would be disposed at right angles to wheel 84 and wheel 83 would lie in the plane of Wheel 85. Then the wheel 84 would not rotate and the motion of the carriage would be parallel to the rails and at a speed determined by peripheral speed of intermediate driving wheel 83, while wheel 82 would slide on the serrated surface of wheel 84.

If, because of a change in the direction of the pattern, the steering motor should rotate the spindles 80 and 8I to place the wheels 82 and 83 in the positions shown in broken lines, then the wheel 82, whose peripheral speed is indicated by the vector 1) will drive the wheel 84 at a speed corresponding to the component of the speed of the wheel 82 parallel to the rail I8, this being indicated by the vector 0. At the same time,

the wheel 83, whose peripheral speed is represented by the vector d (which is equal to vector 1)) will drive the wheel 85 at a speed corresponding to the component of the speed of wheel 83 in a direction parallel to the track 30 as indicated by the vector e. The resultant motion of the carriage is the sum of the vectors 0 and e, which is always equal to vector b and to vector d; the motion is therefore in proportion to the common peripheral speed of the wheels 82 and 83. Thus, the resultant motion of the carriage due to the engagement between the drive wheels 89 and 52 and the rails I8 and 30, respectively, will be in the same direction as the vectors 2) and d and hence parallel to the planes of wheels 82 and 83; the speed of the carriage, however, will be reduced in proportion to the relationship between the diameters of the drive wheels 89 and 52 and the diameters of the wheels 84 and 85. While the direction of the motion of the carriage varies in accordance with the pattern being followed, the lineal speed will remain constant so long as the rotational speed of the wheels 82 and 83 remains constant.

To provide a driving connection between the driving motor 15 and the spindles 80 and BI and hence the intermediate driving wheels 82 and 83, the driving motor I5 is mounted on the underside of the upper member 95 of the carriage body and has its shaft I05 projecting upwardly through the member 95. The upper end of shaft I05 is provided with a pulley I06 which drives spindle driving pulleys I01 and I08, for spindles 80 and 8|, respectively, through belt I00, see Figures 6, 7 and 9. Inasmuch as pulleys I01 and I00 are of the same size, they will be driven at the same rotational speed.

Steering motor I0 is also mounted on the underside of the upper frame member 05. The lower end of the motor shaft I8 projects beneath the bottom frame member and carries the tracer II; the upper end of the shaft carries the sprocket IIO which, through the chain III, drives the steering sprockets H2 and II3 of the spindles 80 and SI, respectively. If desired, the sprocket IIO may be provided with an annular rubber insert IIOa to dampen small vibration of the steering motor before the vibrations are transmitted to the spindles. Thus, rotation of the shaft of the steering motor will rotate the steering sprockets H2 and H3 and the tracer 'II through the same angular distance, for the reason that the tracer is connected directly to the shaft and the sprockets H0, H2 and H3 are all of the same size. The pulleys, sprockets,

belt and chain are all enclosed within a suitable housing II4.

The driving and steering actions of the motors l5 and I5, respectively, are transmitted from the driving pulleys I01 and I08 and the steering sprockets H2 and II3 through the spindles and BI. Spindle 80 is illustrated on an enlarged scale in Figure 10 of the drawings; inasmuch as the spindles are of identical construction, only spindle 80 is described in detail herein. As shown in Figure 10, the spindle comprises an outer sleeve II5 secured as by a set screw H0 in the boss III which extends downwardly from the member 95. Sleeve II5 supports suitable ball bearings I I8 and I I9. which in turn rotatably support the inner sleeve I20. The upper end of the inner sleeve I20 is keyed to sprocket I I2, and at its lower end sleeve I20 carries a housing I2I in which the intermediate driving wheel 82 is mounted. Thus, rotation of the sprocket H2, in accordance with rotation of the steering motor 16 transmitted through the chain I I I, will result in corresponding rotation of the inner sleeve I20 and corresponding steering movement of the intermediate driving wheel 82.

The driving effort of the driving motor I5 is transmitted to the intermediate driving wheel 82 through the shaft I25 to the upper end of which the pulley I0'I is secured as by a set screw I26. Shaft I25 is supported near its upper end by a ball bearing I21 secured at the upper end of sleeve I20 by a cap I28 which is mounted on the hub portion I29 of the sprocket II2 by suitable recessed head screws I30.

The lower end of shaft I25 is supported by a ball bearing I3I carried in a recess in the enlarged lower end I32 of the inner sleeve I20. A worm I33 is secured to the lower end of shaft I25, a spacing sleeve I34 being interposed between the worm and the lower face of the bearing I3I The drive to the intermediate driving wheel 82 is through a gear train made up of the worm I33, worm wheel I35, pinion I36, gear I31 and gears I38 and I39. Gear I39 is mounted on shaft I40 which supports the drive wheel 82, worm wheel I35 and pinion I 35 are mounted on the shaft III, and gears I31 and I38 are mounted on shaft I42. All of these shafts are supported by suitable bearings in the housing I2I. The housing is clamped to the lower enlarged portion I32 of the inner sleeve I20 so that steering motions of the sleeve I20 will be transmitted to the housing. In order to prevent lubricant from the gear train reaching the intermediate driving wheel 02, a shield I43 is secured to the interior of the housing and extends over the upper portion of the wheel 82.

In order to provide for easy assembly of the carriage and also to provide a convenient means for disconnecting the carriage driving and steering mechanism, the upper frame member 95 of the carriage, which supports the driving motors, spindles 80 and BI and associated mechanisms, is formed separately from the bottom frame member 50 on which the wheels 5I and 52 and friction wheels 84 and 85 are mounted. As shown in Figures 6 and 7, the members 50 and are held in alignment by four posts I45 extending upwardly which are pressed into downwardly extending bosses I46 of the member 05 and slidably mounted in upwardly extending bosses I41 on the member 50, bosses I46 and M1 having aligned bores. Thus, the upper and lower frame members are held accurately in alignment by the posts, but the upper member may be raised and lowered with respect to, the lower member.

In order to limit the downward movement of the posts I45 in the, bosses I41 and thus to determine accurately the desired lower position of the frame member, adjustable stops, comprising set screws I48, are threaded into thelower portions of the bores of the bosses, I41. The upper ends of the set screws I48 engage and support the ends of the posts I45 as shown particularlyin Figure 6, and the set screws may be locked in the desired position of adjustment. by lock nuts I49.

In service, the set screws I48 are adjusted to a point at which the frictional engagement between the intermediate driving; wheels 8.2 and 83 and the friction wheels 84 .and 8.5. is sufficient to provide adequate driving force for the carriage without substantial slippage in directions parallel to the planes of the wheels 84 and 85, but at the same time, not great enough to impose undue resistance to slippage of the wheels 82 and83 across the faces of the wheels 84v and 85. Proper driving engagement can be obtained readily with intermediate driving wheels composed of fairly hard rubber or the like andwi-th wheels 84 and 85 preferably made of a metal such as hardened steel, with axially extending serrations on their driving faces as shown at Ma and 85a. The serrations prevent slippage circumferentially of the wheels, while transverse slippage can tak place as easily as with a smooth-faced wheel.

In order to cushion the downward movement of the upper carriage member 95, I. employ springs I50, surrounding the posts I 41, the ends of the springs engaging the horizontal end faces of the opposed bosses I45 and I46.

To provide a conventient means for raising the upper frame member and thus disengaging the wheels 82 and B3 from the wheels 84 and 85, pairs of links I5I and I52 are pivoted at opposite sides of the lower frame memberiil and upper frame member 95, respectively. The ends of these links are connected as shown particularly in Figures 6 and '7 by intermediate links I53, the total length between the pivot points of each set of links I5I, I52 and I53 being greater than the straight line distance between the points of connection of the links I5I and I52 to the frame members 55 and 95 when the frame member 95 is in lowered position so that rotation of the intermediate link in the direction to bring the pivot points into alignment will raise the upper frame member 95.

The links I53 are preferably rotated to raise and lower the upper framemember 95 by means of pairs of parallel links I54 and I55, the ends of which are pivotally :mounted on a collar I56 supported in a bearing I561: on the carriage member 55 and slidable on a square shaft I51, the ends of whichare supported by the end frame members 28 of the sub-frame?! (see Figures 3 and 8) Opposite ends of shaft I51 are provided with handles I59 within easy reach of the operator of the machine. Angular movement of the handles in the direction of the arrow in Figure '7 will raise the upper member 85 through the action of the shaft I56, links I54 and I55, and the intermediate links I53, acting on links I5I and I52. The arrangement is such that the links I53 may be rotated slightly beyond the point required.to bring all of the pivot points in direct alignment, in which position the upper link I54 engages the rod I55, thereby preventing further rotation of the rod, further movement of links I54 and I55 and further rotation of the intermediate links 10 I53, thus locking the upper frame member in raised position.

With the upper frame member in raised position, the drive wheels 52 and 53 are disengaged from the wheels 34 and 85, and the tracer I7 is disengaged from the pattern. Thus the carriage can be moved freely in any direction, and patterns can be replaced or moved on the pattern support without difficulty. When the upper frame member is lowered, the intermediate drive Wheels 52 and 83 engage the friction wheels B l and $35 with the proper amount of force as determined b-y adjustment of the set screws M8 and the tracer point "(1 engages the pattern 26, thus placing the device in condition for operation.

Automatic Zine fol-lower control.

As noted above, the steering motor '75 is controlled to steer the carriage in such a manner that the tracer point I? will move along the contour C of the pattern 25 with a predetermined amount of overlap maintained between the tracer point and the contour. This result is preferably accomplished by employing a conductive pattern and controlling the steering motor by variations in the flow of current between the pattern and. the tracer, the circuits being arranged to steer the carriage to maintain the flow of cmrent between pattern and tracer substantially constant. According to the forms of the invention disclosed in the present application, this may be accomplished either by a circuit responsive to changes in the resistance to flow of current between the tracer point and the contour or pattern, or in another form wherein the tracer point is vibrated in a direction substantially transversely of the contour, by a circuit responsive to changes in the point in the vibratory cycle of the tracer point at which the tracer point makes and breaks contact with the conductive contour. The resistance method embodying the tracer point shown in Figure 12 and the electrical circuits shown in Figure l l will be first described.

A preferred tracer point construction isillustrated in Figure 12 as comprising a member I55 composed of insulating material and suitably secured to the shaft '18 of the steering motor I5 and ccnstituting'in effect, an extension of that shaft. This member I55 carries two slip-rings Ilil and IE2 engaged by brushes I53 and I64 which are supported bya block of insulating material I65, which in turn is carried by the lower frame member 55 of the carriage 3I. A pin I55 coaxial with the shaft 18 is pressed into the block I60 and supports another cylindrical insulating block I5! which is also coaxial with the pin'and motor shaft. The upper end ofthe block I51 carries a brass ring I58, and a contact ring I59 is slidably mounted on the lower end of the block; the ring is urged downwardly by the spring [75 which surrounds the block It! and is preyented from being pushed off of the block I51 bythe inwardly extending flange III which engages the shoulder H2. The contact ring I55 is connected to slip ring I52 through the spring I16, brass-ring t58 and conductor I13. I V

The tracer point '51 is slidably mounted in the block I61, being slightly offset from the center of the block as shown. The tracer point I! has a head Ilfi which operates in an enlarged recess its in the block I61; the spring I15 disposed within the enlarged recess urges the tracer point down into engagement with the pattern. The upper end of the spring engages a metal plug I'I'i pressedinto the end of the recess, and the electrical connection between the tracer and the slip ring itI is made through the spring I16, the plug Ill and conductor I19 which extends within the insulating block I99.

As shown in Figure 13, the contact ring 159 engages the contour C near the point of engagement of the tracer point IT with the contour. The control circuit is arranged to control the steering motor in response to variations in the resistance to flow of current between tracer point and contact ring, which variations are caused by changes in the resistance to flow of current between the tracer point and contour, the changes in resistance resulting from changes in the amount of overlap between tracer point and contour. The distance between the contact ring and the tracer point, and the resistance of the contour C are such that the slight variations in distance along the contour between the tracer point and the contact ring, which may take place as the tracer travels along the contour, do not make a suiiicient change in th resistance of the circuit as compared to the changes in the contact resistance between tracer point and contour due to variation in the amount of overlap between tracer and contour to be of sufficient consequence to be reflected in the control.

The control 01 the steering motor is preferably accomplished by the circuit arrangement shown in Figure 14 wherein the various components are illustrated diagrammatically (in order to simplify the diagram, the filament circuits are not shown in this figure or in Figure 18) the same reference characters being applied to components of the driving and steering mechanisms, such as the motors, spindles, driving wheels and the like, and to the tracer point and contact ring as were used in the previous description. Thus, the driving wheels 82 and 83 of the spindles 89 and iiI are driven at substantially constant speed by the driving motor indicated at I and embodying an armature 75a and field 152), the mechanical connections between the motor and the spindles being indicated by broken lines.

Similarly, the spindles 89 and BI are steered by the steering motor I6 embodying armature 16a and fields 16b and 160, the fields being wound so that when one field is energized, the steering motor will rotate in one direction, and when the other field is energized, the steering motor will rotate in the opposite direction. The connections between the steering motor and the spindles 80 and BI and the tracer point I1 are indicated by broken lines, the arrangement, as previously described, being such that the spindles and tracer point are rotated simultaneously by the steering motor so that the planes of the driving wheels 82 and 83 are always parallel to a plane passing through the center of the tracer point and the axis about which the tracer point is rotated.

A portion of the contour C to be followed by the apparatus is shown in the drawing as being engaged by the tracer point H and the follower ring I69. The contour C may comprise a heavy line drawn with a graphitic ink on paper, whereas the tracer 11 may have a rounded hardened steel point. Thus, varying amount of overlap between the tracer and the line causes a corresponding change in the point-to-contour conductivity. In a preferred form of the invention, the materials are such that the point-tocontour resistance changes from about 5000 ohms at full contact to infinity at no contact over a distance of a few thousandths of an inch. The

changes in area of contact produce a gradient in conductivity, and the circuit is so arranged that when the point-to-contour resistance exceeds a predetermined amount, the steering motor is energized to steer the carriage and tracer point in toward the center of the pattern to increase the amount of overlap, and when the resistance is less than a predetermined amount, the other field of the steering motor is energized to rotate the steering motor in the opposite direction to steer the tracer point and carriage in the opposite direction, thereby to reduce the amount of overlap between the point and contour.

While, as noted above, this change in resist ance is preferably provided by employing a metal point having a relatively low resistance in combination with the line composed of a relatively high resistance material such as graphite on a non-conductive background, it will be appreciated that a metallic pattern, such as a thin metal foil on non-conductive background, may be employed in conjunction with a tracer point composed of graphite or other suitable material having a relatively high resistance, which will also give the desired variations in conductivity with variations in the point and contour overlap.

Essentially, the control of the steering motor is accomplished by making the point-to-ccntour circuit an element of a phase selective bridge which controls the firing of two electronic tubes, one tube controlling the energization of the motor for rotation in one direction, the other tube controlling the energization for rotation in the opposite direction. In the present example, each tube supplies the energization of one of the motor fields. With the point-to-contour resistance below a predetermined value, one field predominates; with the resistance above that value the other field predominates, and when the resistance equals the predetermined value, 1. e., at the null point, both fields are energized substantially equally.

Assuming the main power control switch we, the manual starting control switch I91 and the starting relay I92 to be closed, energy is supplied to the steering motor 16 from the A. C. power supply lines I93; the steering motor is energized through the power supply transformer Hi l and the control currents are supplied through the control transformer I85, the primaries I36 and I BLrespectiVely, of these transformers being connected in parallel across the main power supply line.

The phase selective bridge comprises the secondary I88 of the transformer I across which is connected a potentiometer I89 having its sliding contact I99 connected at point I 9| to the end of the three series resistors I92, I93 and I94, which are substantially equal in resistance, and resistor I94 being connected at point I95 to one end of potentiometer I89 and secondary I88. Resistors I92 and I93 have their common terminal I96 connected through the phase shift bridge I91 and the damping net work I98 to the cathodes of thyratrons I99 and 299 which control the energization of motor fields 15b and 790 to cause rotation of the armature 75a in the desired direction.

The grids of thyratrons I99 and 299 are connected to points I9I and 20I at the ends of re sistors I92 and I93, respectively. Point ZilI also is connected to the tracer point 11, while point 295 at the end of potentiometer I69 is connected to the contact ring I69. By this arrangement the grids of the thyratrons reverse in phase relative to their center point I86 as the. tracer and template change. from a condition of no contact and infinite resistance to complete contact and a resistance of, for example,-5000 ohms. This action may be explained by assuming that transformers I84 and I85 are phased so that potential measured from'point I95 toward point. 205 is negative with reference to. the plate voltage on the thyratrons :99 and 2.00. At open circuit, with the tracer point II out of contact with the contour C, the three resistors I92, I93 and I94 are connected across the section of the potentiometer between sliding contact I90. and point I95. The voltage drop through this portion of the potentiometer maybe, for example, 18 volts as marked on the drawing, and this voltage will be about equally distributed on the three. resistors I 92, I93 and I94. The point; I96, therefore, will be about 12 volts negative. with respect to point I95, while point 20I will bev 6 volts negative with reference to point I95, and point I'9I will be 18. volts negative with reference to point: I95. Thus, with reference to the grid center point I96, point 'ZO-I will be 6 volts plus, and point I9I will be 6 volts minus. Under such conditions, the tube 200 will fire while the tube I99 will be held non-conductive by the negative potential applied to its grid. Firing of tube 209 will energize the circuit through field l' bc causing the armature 16a of the steering motor IE to rotate in a direction to steer the carriage and rotate the tracer to increase the amount of. overlap between tracer and contour, i. e., in the example shown in the drawing with the tracer traveling along the contour in the direction indicated by the arrow, the motor will operate to turn the tracer point and the spindles B and 8| clockwise.

In the opposite condition, that is, with the maximum overlap and minimum resistance between tracer and contour, the full secondary voltage, except for the drop due to the point-tocontour resistance, will be across resistor I94. Resistors I92 and I93 will be connected across the section of the potentiometer between the slider I95 and the point 205, the voltage across this portion of the. potentiometer being, in the example given, about 12 volts as marked on the drawing. Inasmuch as the point 205 at the negative end of the potentiometer is connected to the point 2m, and the slider I99 is connected to the point ISI, the conditions will be reversed as compared to the previous example, and point 2M will have a potential of minus 6 volts with respect to the center point lfiii, whereas point I9I will have a potential of plus 6 volts with respect to the center point I36. Under these conditions, tube I99 will fire while tube 209 will either be held non-conductive or fire very late in the half cycle depending upon the amplitude of the control voltage, current will flow through the field 751; of the. motor and the motor armature 16a will rotate in a counterclockwise direction, decreasing the amount of overlap between the tracer and the contour.

As the amount of overlap decreases from maximum, the increasing point-to-contour resistance will reduce the positive voltage applied to the grid of tube I99, and the voltage applied to the grid of tube 259 will become less negative. Tube I99 will thus fire later in the positive half cycles of plate voltage applied toit, and tube 29!] will begin to fire late in the positive half cycle of its plate voltage or to fire earlier if it had been. firing toward the. end of the. half cycle, until the null point. is reached when both tubesv will fire for equal portions of: the half cycle. The. null point. occurs when the resistance between the point and pattern becomes substantially equal to. the resistance of resistor I154. Under such circumstances, the bridge will be balanced and both. tubes will fire at. about. the same point in the. samepositive half cycle by reason of the voltage applied by the phase. shift bridge H1.

The. phase shift bridge Ii9'f is employed to ob-- tain a. smooth application of power in. the steering motor circuit, with the power substantially in proportion to: the. conductivity between the tracer point and contour, and hence in proportionv to the. amount of displacement of the tracer from the: null point. The bridge I91, which comprises. transformer 2&8, resistor 2.09 and, condenser ZI'B, is connected between the center .point I96 anclthe. cathode power supp y line 2-H. This normally supplies to. the grid control circuit a voltage lagging the plate voltage of the thyratrons. by about degrees.

The combination. of the constant amplitude lagging voltage. produced by the phase shift bridge I91 with the. in-phasev voltage produced by the phase selective bridge, produces a resultant voltage advanced with respect to the lagging voltage, the amount of advance depending upon the amplitude of the voltage produced by the phase selective bridge. Thus, in the. extreme condition of no contact between tracer and contour orthe extreme condition of complete contact between tracer and contour, the. amplitude of the voltage produced by the phase selective bridge will be such that thyratron. I99 or thyratron 208, as the case may be, will firethroughout substantially all of the positive half cycle of its plate voltage. As. the amplitude decreases, the tube will fire at a later point in the cycle, resulting in the. application of less power to the motor, and the control voltage of the non-firing tube will approach the critical voltage more closely. At the null point, where substantially no voltage is applied by the phase selective bridge, both tubes will fire as a result of the voltage applied by the phase shift bridge I91, but as this voltage lags. the plate voltage by about 90 degrees, the tubes will fire only in the latter part of the positive half cycles of plate voltage.

Inasmuch as both tubes fire on the same positive half cycle, under such conditions fields Ito and T60 will both be energized. Theoretically, these fields should balance each other so that there should be no resultant motion of the motor when the tracer is at the null point. Practically, null conditions exist only momentarily, the. normal response of the motor being a continuous succession of small adjustments to a null from which there is an immediate departure because of further movements of the tracer. Thus, there is a slight vibration of the motor under conditions which approach the null, but this. vibration is so slight and the net power developed by the motor is so small, that there is substantially no motion transmitted either to the tracer point or to the spindles 8i) and ill when the tracer is following a straight line. If desired, a resilient connection, such as the rubber ring Ilfla in the sprocket IIIl, may be interposed between the steering motor and spindles 8D and 81 to absorb slight successive ad- Such a aezaeri resilient connection will not efiect the response of the device as it follows a curve, or under any condition requiring a substantial correction.

It is to be noted that a correcting impulse is supplied to the motor during each cycle of the applied current; thus, with the usual A. C. power supply there is a correction, if one is required, 60 times a second. Thus, corrections are made so frequently and with so little intervening travel of the carriage, that no large deviations from the null are permitted to occur, whether the tracer is following a straight line or a curve.

As noted above, with a rounded point, hardened steel tracer and a heavy graphite line on paper, the point-to-contour resistance varies from in finity at no contact to about 5000 ohms at full contact. It is desirable that the relationship between the point-to-contour resistance and the resistance of the resistor I95 be such that the null point, where these resistances are equal, will occur in a zone where the point-to-contour resistance varies at a reasonably uniform rate for given changes in overlap. I have found satisfactory results to be obtainable with 30 volts across the potentiometer I89 and with the resistors I92, H93 and I94 all having resistances of approximately 100,000 ohms. Such a circuit balances when the point-to-contour resistance is approximately 100,000 ohms; with a point and contour of the character described, this resistance corresponds to a point and contour overlap of approximately thousandths of an inch. This arrangement gives a smooth control whereas, for example, if the resistance of the resistors I92, I93 and I9 3 were as much as a megohm, for example, the efiect would be similar to ofi-on control, and the throttling eifect of the varying point-to-contour resistance would be lost; such a control would not be as smooth as the preferred form and would be subject to difficulties because of hunting.

Conversely, if the resistance of the resistors I92, I93 and I94 is made too low, as compared to the minimum point-to-contour resistance, then the control will lose sensitivity, and the tracer will wander over the contour with a considerable loss in accuracy, and the currents flowing through the phase selective bridge and the pattern will be greater than necessary. Obviously, the resistances used must be governed by the resistance characteristics of the tracer and template materials.

The varying conductivity in the point-tocontour circuit tends inherently to eliminate oscillation in the steering motor and hunting of the controL, However, to minimize further the hunting tendency inherent in most servomechanisms, I preferably employ the damping net work Hit in the thyratron cathode circuit. This net work comprises resistors 2I5 and H6 connected to the cathodes of thyratrons I99 and 209, respectively.

During conduction through either thyratron, a potential drop substantially greater than the critical grid voltage occurs across its cathode resistor. A corresponding charge is accumulated on condenser 2 H which has the effect, upon subsequent discharge, of depressing or reducing the grid control voltage for the tube which has just fired; that is, the charge on the condenser makes the cathode of the tube which has just fired less negative with respect to its grid and hence has the effect of delaying the firing of the tube on the succeeding positive half cycle. For example, as sumo conditions to be such that tube 299 is conducting, the voltage drop across resistor 2I6 will produce the polarity indicated in the drawing,

and a charge of corresponding polarity will appear on condenser 2 I "I. The charge on condenser 2 I I will not entirely dissipate during the immediately succeeding negative half cycle during which both thyratrons are non-conductive. The efiect of the charge on the next positive half cycle is to depress the control voltage for tube 290 and elevate it for tube I99.

This effect is small in comparison to the control voltage impressed on the grids in response to a large deviation from the null point so that it does not seriously limit the rapid response of the control to conditions such as occur at a sharp turn. However, as the null point is approached and the control voltage created by the phase selective bridge approaches the critical voltage, the voltage of the condenser becomes effective to reduce the power transmitted by the tube which has been fired, and to place the tube which has not been firing in condition where a close approach to the null will result in an anticipatory correcting im pulse. This feature of the control is particularly effective in stabilizing the adjustments for small deviations such as may occur as the tracer follows along a line that is substantially straight or smoothly curved.

The relationships between plate voltage, the lagging voltage produced by the phase shift bridge and the grid control voltages produced by the phase selective bridge are shown diagrammatically in Figure 15, in which diagram A shows the plate voltage Ep on tubes I99 and 2&0, the critical grid voltage E0 of the tubes and the voltage a supplied by the phase shift bridge I91; diagram B shows the voltage 1) between points 2IJI and I95 under conditions of no contact between point and pattern, and the voltage 0 between points I9I and I99 under the same condition. Under these conditions, the grid voltage applied to tube 209 during each positive half cycle is the resultant of the voltages a and b and is indicated by the curve (1+!) in diagram C. It will be noted that this voltage exceeds the critical voltage in the early part of the positive half cycle. Hence the tube 200 will fire and will be conductive throughout the major portion of each positive half cycle as indicated by the shadin so long as there is no contact between the point and the pattern. Under the same conditions, the voltage applied to the grid of tube I99 will be the resultant of voltages a and 0 shown at a+c in diagram D. As there indicated, this voltage exceeds the critical voltage only in the latter part of each positive half cycle of the plate voltage. Hence tube I99 will fire late in the cycle, and very little power will be supplied to field 1617.

As the contact between point and pattern increases and the resistance decreases, the amplitude of voltages b and c gradually decreases. This results in firing of the tube 299 later in the cycle and tube I99 earlier in each cycle until the null point is reached when the phase selective bridge is balanced and the grid voltage on both tubes is the voltage it produced by the phase shift bridge I91. Under these circumstances, both tubes will fire at about the mid-point of each positive half cycle of the plate voltage as indicated by the shading in diagram A, the power supplied to both field windings will be substantially equal, and the motor I6 will remain substantially stationary.

If the amount of overlap between point and pattern increases beyond the null point, then the curves b and c in diagram 13 are reversed in position and the effect on tubes I89 and 299 is reversed with tube I99 firing through a greater portion of 17 the; cycle .than tube 200. When the point of minimum resistance is reached tube I99 will fire early .in the cycle (as shown in diagram for tube 200) and tube 200 will fire late in the cycle (as shown in diagram D for tube I99).

The effect of the damping network I98 is also shown in diagrams C and D of Figure 15. As described above, after the first half cycle of firing for either tube, the damping circuit has the effect of reducing the grid voltage applied to that tube. Thus, as the charge on the condenser 27 builds up, the curve a-l-b which is the grid voltage of tube 200 will, in effect, be moved downwardly to the position shown in dotted lines, thus delaying the firing of the tube 200. At the same time the grid voltage applied to the tube I99 will be madeless negative, having the effect of raising the voltage a+c as indicated by the dotted line curve in diagram D, thus advancing the time of firing oi the tube I99. The result, therefore, is to slow down the correcting movements of the steering motor as the correction is being completed, thus preventing over-shooting and hunting, yet the control does not diminish the power initially supplied to the motor in response to a change in point-to-contour resistance; thus, corrections are made promptly and with ample power. Obviously, the effects of the damping circuit will be reversed when tube I99 fires early in the cycle and tube 200 fires late, as occurs when the overlap between point and pattern exceeds the null point.

Starting control In starting the apparatus, it is desirable -to-begirrthe cut awayirom the pattern and proceed in a straight line to the contour to be followed. This mode of operation requires that the steering motor be inoperative-until the tracer contacts the contour, for reason that if the steering motor were operative it would, tend to continuously rotatein a clockwise. direction, in the em bodiment shown in the drawing, so long as the tracer remained out of contact with the contour.

To accomplish this result, as well as to control the starting of the drive motor I andthe applicationof the high pressure oxygen, I employ the double polemanual starting switch I8 I the magneticcontactor I82 and, thyratron 220 Assuming the main line switch ISO to be closed, closing of the switch IGI completes the circuit through contacts,.il2l,v thus completing the power supply to the driving motor through a speed control circuit-tobe described below, and energizing the sgjlenoid valve 222 which opens to supply high pressure oxygen to the torch 35. Before the switch is closed, the spindles 89 and ill are turned to point, the intermediate driving wheels 32 and 83 toward the contour. This may be done with the intermediate wheels in contact with the wheels 84 an d 85,-or raised out ofcontact with them by the handle I59 and associated mechanism. With the-intermediate wheels in raised position, the carriage easily can be moved-to anydesiredstarting position. When the switch It! is closed, the drive motor'moves the carriage toward the contour,which movement continues in a substantially straight. line. until the contour is reached, Whereupon-theautomatic contour following control is placed in operation.

The-automatic control is initiated through the thyratron..2201 and ;the magnetic relay I82, So long as .the relay .I 82'is not energized, the vcircuit through; the ,contacts .223 remains. open, thus no powerlis supplied .to the, cathode...supply conductor iZ-II vfor the-.thxrratrons; I 99. and 2280 1: and no 1 8;:- power can'be-supplied to the steering motor I6. The circuit is arranged so that thyratron 220 remains non-conductive until the tracer touches the contour. This isaccomplished by connecting the gridof thyratron 220 to point I9I through the gridresistor 224, the power supply for the thyratron "220 being supplied by thesecondary 225 of transformer I through the coil 22$;a-ndcontacts221- of the magnetic contactor I82-andthe contacts 'ZZB-Of -themanual contactor I8I:, the leadfromcontacts- 228 extending to the point I96. So long as the tracer'is out-of contact withthe contour, point I9I is;negativeto-point I96as previously described, and accordingly, the tube 2'20 is held non-conductive. However, as soon as the tracer touches the contourand makes sutficient contact with it to reducethe point-tocontour resistance-to a value such that point I9 I is negative with respect to-point I96 by anamount less than thecritical voltage of the tube 20fl-;(the critical voltage ordinarily being about minus 3 volts), the tube; 220- willfire, operating relay I82. 'Thecontacts of'the relay are thus closed as, or slightly before, the -tracer reaches the null point'on the-contour and afterthe traceris 'in contact with the contour. Movable contact 229 of relay IB-Zfirstcloses the circuit through: contact 23D- and then-opens the circuit through contact 221. Thus, the'movable contact 229 cuts out the cathode of-thyratron 22!! and renders it ineffective immediately after the holding circuit through resistor 23I has been completed. At the same time, the circuit through contacts 223" is completed, thus puttingthe automatic control of the steering motor into operation, and this control will be maintained until the manual switch I BI is opened," at which time the relay I82 will drop out, the driving motor willstop and'valve 222 will'close, thus resetting the starting control for another operation. 1

Drive.. motor .spced contr ol In orcler to secure uniformity of action of the cutting torch, it is desirable that the speed of movement of the torch over the work be maintained at a substantially constant value, say it infiv e cen s al ece ar o y the speedier differentthicknesses of work, difere i mat r als, ifierent gas p s e a the like. To permit reasonably wide adjustments in speed of the driving motor and at the same t me ac ra e y igma nisin. hed s ed. mear referably employ the drive motor speed control circuitshown in Eigure 1 4 of. the. draWin sand p isina m-, ect fie 3, ;c n e e tress the A. C. supply linelESandmaintaining asubstantially' constant voltage-across the potentiometer 2-3 6, thevol'tage.beingsubject only .to fluctuations in line; voltage. A, relatively large filter con denser.,23l is also connected acrossltheupoi entiometer. The field .Lfiboof. motor 15 is separately excited. by connectionthrough rectifier 23,8 to the, A. C-npowerlinewhen. thecontacts 22I ;of .-the manual. startingnswitch I8I are closed. At the same time,.theiarmature L515 energizedbycurrent flowing through the thyratrOILZS 9, anreactor 240 being connected in series ,in the thyratron circuit tolimit the .current flow. The gridpf thyratron 2 39 .is.connected through a resistor 2M to the sliding contact 242 of potentiometer 2.3.

When the tube 239isconduetive, thepolarity across -the. armature will be. as indicated, in the a t wil be ppa en atri t e a m.- ture voltage is below the voltageonthepotenti ometer between the point 243.ar ,d the,. idin contact 242, the grid will be held plus by the difference between the voltages. If the armature voltage is above that value, the grid will be held minus by that diilerence. Thus, conduction of the tube 239 will be stopped when the armature voltage exceeds the voltage between point 243 and slider 242 by an amount just in excess of the critical voltage of the tube. Whenever there is a positive grid, the tube 239 will be fully conducting, giving maximum torque at any speed.

The field excitation is substantially constant so that the armature voltage is nearly proportional to its speed. Thus, by moving the slider on the potentiometer, a corresponding change in speed can be obtained and the potentiometer can be calibrated in inches per minute of travel of the carriage.

The motor speed is maintained substantially constant inasmuch as an increase in line voltage causes the strengthening of the motor field and at the same time an increased voltage on potentiometer 236. Conversely, a decrease in line volt age decreases the strength of the motor field and decreases the voltage on the potentiometer. These changes in line voltage and potentiometer voltage tend to counteract each other insofar as the speed of the motor is concerned. Hence, ordinary fluctuations in line voltage do not substantially affect the motor speed.

The knob 244 shown on panel 54 (Figure 2) controls the potentiometer and provides manual control of the motor speed. The controls are such that the operator has only to set the motor speed control at the desired value, light his torch to start his cut a small distance away from the contour to be followed, adjust the wheel 62 and 83 so that they point toward the contour preferablyin such a manner that the tracer will intersect the contour obliquely, and then, when the work has been preheated sufficiently, close the switch [8| (which is also mounted on panel 54), thereby starting the drive motor and turning on the high pressure oxygen. The carriage will then proceed in a substantially straight line until it reaches the contour when it will automatically follow the contour at a substantially constant speed until the operator opens the switch IBI. When the switch [8| is opened, the drive motor will stop and the high pressure oxygen will be shut ofi, thus stopping the cutting a action.

Automatic control embodying a. vibrating tracer Instead of the tracer and control circuit just described, I may utilize an arrangement in which the tracer point is vibrated across the contour transversely of the direction of movement of the carriage. In this type of apparatus, the desired throttling efiect and stability of operation are obtained not by variations in the point-tocontour resistance as in the case of the previously described form of the invention, but by changes in the time in the cycle of vibration of the tracer point at which substantial contact with the contour is made or broken. This type of control does not depend upon variations in point-to-contour resistance for different amounts of overlap and hence can .be employed with metal patterns on non-conductive base or background materials; for example, thin foil patterns on paper may be used with metal tracer points. The high resistance contour and tracer point combinations heretofore described may also be employed with this circuit, however.

The vibrating tracer point control may be used with the carriage previously described, the only change required being in the support for the tracer point, which, as shown in Figures 16 and 17, comprises a cylindrical block 245 secured to the shaft 18 of steering motor 16 as by a set screw or other convenient means. This block supports slip rings 246, 241 and 246 engaged by brushes 249, 250 and HI, respectively, and at its lower end supports a plate 252 composed of insulating material to which the oscillating motor'253 is secured by means of screws 254 and 255 and plates 256. The motor preferably is of the type described in my issued Patent No. 2,351,623, issued June 20, 1944, and embodies a field structure 251 and a pivoted armature 258. As described in my said patent, motors of this type vibrate in synchronism with the'frequency of the applied current rather than at twice the frequency of the applied current as is customary with ordinary vibrators. Motors made according to my patent ordinarily embody two salient pole faces. For the present purposes, one of the pole faces of the field structure is cut away, leaving only the salient pole face 259. For reasons which will appear below, the current supplied to the motor is put through a half wave rectifier, and with the arrangement shown, each half cycle applied to the motor will attract the armature toward the pole face 259.

The armature is pivoted to the field structure as at 260; the pivot pin 26I extends beneath the armature structure and supports a lever 262. Near one end of the lever 262 there are two upwardly extending pins 263 which are disposed on opposite sides of a fiber plate or vane 264 projecting from the rear end of the armature 259; vibration of the armature thus vibrates lever 262. The other end of lever 262 carries the tracer 265 which is urged downwardly by a, spring 266 within the housing 261. The tracer is slightly offset from the center line of the shaft 18; themotor is arranged to vibrate the tracer in directions across and substantially normal to a line extending from the axis of shaft 18 to the mid-point of the travel of the tracer.

A conductor ring 269 surrounds the tracer and is supported by a spring member 269, the member 269 being supported by the insulating member 270 which also supports the brushes 249, 250 and 25!. The member 210 is supported from the bottom frame member 69 of the carriage. Power to operate the oscillating motor 253 is supplied through suitable conductors leading to the brushes 249 and 250, through them to collector rings 246 and 241 and thence to the motor through suitable conductors extending within the insulating block 245. The circuit to the tracer is through the brush 25!, collector ring 248, and a conductor leading to the motor 253 on which the tracer is conductively mounted through pivot 26!, lever 262 and spring 266. The circuit to the ring 268 is through the spring 269 and a suitable conductor secured thereto.

The steering motor control circuit for a device embodying the vibrating tracer is shown in Figure 18. In this figure, the starting control and the drive motor speed control are the same as previously described, and the same reference characters have been applied to these components as were used in the description of Figure 14. The steering motor is the same as previously described, consisting of the armature 16a and fields 16b and 160, the energization of the fields being controlled by thyratrons 200 and I99 as before.

The arrangement is such that energization of 

